1. Field of the Invention
This invention relates to a liquid depositing device for depositing a predetermined quantity of a sample liquid on a chemical analysis element such as a chemical assay slide and a method for carrying out the same. In particular, this invention relates to a liquid depositing device and a method for automatically depositing a sample liquid on a chemical analysis element.
2. Description of the Prior Art
When the concentration of a specific chemical substance in a body fluid, such as blood or urine, of an organism is to be determined by using a chemical analysis element such as a chemical assay slide, one must measure out a predetermined quantity of a sample liquid and deposit it on the analysis element with required accuracy. Liquid depositing devices to be used for this purpose are disclosed, for example, in Japanese Unexamined Utility Model No. 57(1982)-283656, Japanese Unexamined Patent Publication No. 60(1985)-155942, (corresponding to U.S. Pat. No. 4,737,344), British Pat. No. 1,531,760, and U.S. Pat. No. 3,915,651. With these liquid depositing devices, however, it is difficult to change the quantity of the liquid to be discharged from the device by remote control because the position of the stopper for limiting the motion of the piston thereby controlling the quantity of the discharged liquid must be changed.
In U.S. Ser. No. 062,874 (filed June 16, 1987), which is assigned to Fuji Photo Film Co., Ltd., a liquid depositing device has been proposed in which the amount of a liquid to be discharged therefrom can be remote controlled. In this liquid depositing device, a liquid depositing tip is removably mounted on a tip mounting portion formed at one end of a tip support arm mounted for up-and-down movement. A suction-and-discharge mechanism is operatively connected to the liquid depositing tip by way of the tip support arm to suck sample liquid into the depositing tip and to discharge it from the depositing tip onto a chemical assay slide or the like. The quantity of the sample liquid to be sucked into the tip and to be discharged therefrom is controlled by a quantity control mechanism which controls the operation of the suction-and-discharge mechanism. The tip support arm is adapted to move up and down between a sucking position at which the depositing tip is mounted or removed, as required, and the sample liquid is sucked into the tip and a depositing position at which the lower end of the tip is positioned immediately above the liquid receiving layer of a chemical assay slide set at a predetermined position, the sucking position being higher than the depositing position.
However, when the liquid depositing device according to U.S. Ser. No. 062,874 is used in the above-mentioned manner, in some cases the sample liquid is deposited at an improper position or the quantity of the liquid deposited is less than required.
In a conventional device as shown in FIG. 6(a), a liquid depositing tip 15 held by a tip support arm 21 is moved down to a discharging position which is located above a liquid receiving layer 5a of a chemical assay slide 5 by a predetermined distance l, (about 8 mm, for example) after a sample liquid is sucked into the tip 15. At the discharging position, the sample liquid is discharged from the tip 15 in such a way that a drop of the liquid 9a is formed at the lower end of the tip 15. Then the tip 15 is moved down to a depositing position which is closer than the discharging position to the liquid receiving layer 5a. However, the drop of the liquid often rides up the surface of the tip 15 as indicated by the dotted line in FIG. 6(b). In some cases, after a few drops of the liquid have been deposited, the subsequent drop of the liquid discharged from the tip 15 does not land on the chemical assay slide 5.